A stabilizer control device for a vehicle is generally configured to reduce or control rolling movement of a vehicle body by externally applying an appropriate roll moment to the vehicle body by use of the actuation of stabilizer bars while the vehicle is turning. In order to implement such roll stabilizing function, for example, a roll stabilizer for a vehicle described in JP 2002-518245A (hereinafter referred to as Patent Document 1) includes halved stabilizer bars and a turning electromechanical actuator provided between the halved stabilizer bars. Further, an electric motor (motor) and a speed reducing gear mechanism are arranged between the halved stabilizer bars.
In the roll stabilizer according to the Patent Document 1, it is unavoidable for the actuator to have a large size as a whole. Accordingly, a stabilizer control device described in JP 2004-314947A (hereinafter referred to as Patent Document 2) includes an actuator downsized for controlling torsion force of a stabilizer and fully enlarging a single torsion force from a pair of stabilizer bars, and therefore having the minimized size and weight as a whole. Moreover, another type of a stabilizer control device is provided in JP 2005-271828A (hereinafter referred to as Patent Document 3). For example, when the vehicle is running straight ahead on extremely unsteady roads such as rough or bumpy roads even with the electric motor described in the Patent Document 1 switched off for the purpose of stopping the roll stabilizing function, ride quality may be deteriorated by sudden inputs added to the speed reducing gear mechanism from the stabilizer. However, the stabilizer control device according to the Patent Document 3 further includes a clutch mechanism serving as engaging and disengaging device for switching positions of the stabilizer bars from a free position and an engaged position and vice versa, therefore securing a better ride quality without influence on an actuator due to variations of road conditions or the like.
The speed reduction gear mechanism applied in Patent Documents 1 to 3 is known as a general multi-stage planetary gear mechanism. Specially, a known gearing mechanism, which obtains a large gear ratio, is referred to as a harmonic drive gear mechanism (Harmonic Drive.RTM registered by Harmonic Drive System, Inc.) disclosed in the following non-patent document “Principles of the Harmonic Drive Mechanism”, retrieved from the Internet: URL: http://www.hds.cojp/principle/index.html (herein after referred to as Non-patent Document 1). Another known speed reducing mechanism is a paradox planetary gear mechanism. The paradox planetary gear mechanism (a static sun gear and a rotational sun gear) is a planetary gear mechanism in which a pair of internal sun gears with different number of gear teeth is engaged with common planetary gears, for example, as disclosed in the following non-patent document “Theory and Design Calculation Method of Planetary Gears and Differential Gears”, Muneharu Morozumi, Nikkan Kogyo Shimbun, Ltd., Published Apr. 27, 1989, 1st edition, 1st printing, 25-29 (hereinafter referred to as Non-patent Document 2).
Meanwhile, a stabilizer disclosed in JP 2001-260625A (hereinafter referred to as Patent Document 4) includes a viscous coupling arranged between halved right left torsion bars for preventing sudden motional variations of a vehicle while the vehicle is turning so as not to waste suspension strokes of the vehicle. The stabilizer further includes an egageable or disengageable clutch mechanism provided between an outer rotor of the viscous coupling and the right torsion bar for rotating an inner rotor of the viscous coupling. Furthermore, as explained in the Patent Document 4, the viscous coupling includes an operation chamber provided between the outer and inner rotors and filled with viscous fluid, a plurality of inner plates respectively formed in the operation chamber so as to have a predetermined distance from each other in an axial direction while being integrally connected to the inner rotor so as to rotate, and a plurality of outer plates respectively formed in the operation chamber so as to have a predetermined distance from each other in an axial direction while being integrally connected to the outer rotor so as to rotate, wherein shear resistance of the viscous-fluid occurs in the operation chamber in accordance with relative rotations of the inner and outer plates.
The stabilizer control device disclosed in the foregoing Patent Documents 1 to 3 includes the actuator based on an active drive control by the motor. The actuator is connected to the pair of stabilizers via the motor and the speed reducing mechanism so as to add torsion forces to the stabilizer bars. On the other hand, the stabilizer control device disclosed in the foregoing Patent Document 4 is not equipped with a motor and based on a passive drive control by the clutch mechanism. However, for example, in the stabilizer control device according to the Patent Document 4, when the clutch mechanism is configured to be arranged between the pair of stabilizer bars in such a way to be directly connected to the stabilizer bars, a large load is added to the clutch mechanism. Accordingly, an extremely large-size clutch mechanism is required in order to resist the added load, thereby requiring a large-size actuator. Especially, since an end portion of the stabilizer bar must be fixed to a suspension member during installation, the large-size actuator has a disadvantage of installation flexibility due to limitations of space.
In addition, as described in Patent Document 3, the clutch mechanism is connected to the speed reducing mechanism provided in the stabilizer control device where the pair of stabilizer bars is connected via the motor and the speed reducing mechanism. The clutch mechanism is provided in the stabilizer control device and therein connects and disconnects the pair of the stabilizer bars. The clutch mechanism may be downsized but is not applied to the stabilizer control device described in the Patent Document 4.
A need thus exists for a stabilizer control device, which is not susceptible to the drawback mentioned above.